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1、Chapter4 Heredity and variation of bacteria,outline,Concepts Genetic materials of bacteria Mechanism of variation,concepts,Heredity Variation Genotypic variation Phenotypic variation,Variation of bacteria,Variation in morphology and structure lose capsule (Pneumococcus) H O Lose Spore L-form,Variati
2、on,Variation in virulence Bovine TB BCG 13years, 230 generation C. diphtheriae b-corynephage, diphtheriae toxin,Variation,Variation in drug resistance Penicillin resistant strains of staphylococcus aureus Variation in colony S-R Variation in enzyme activity Phenotypic Genotypic,I Genetic materials o
3、f bacteria,Chromosomes Plasmids Phage Transposable elements,DNA forms: ds-DNA, circle,1 Chromosomes,Size E.coli 1300mm, 4288gene Rolling-circle pattern of replication,2 Plasmids,Extrachromosomal genetic elements that are capable of autonomous replication. Small double-stranded DNA molecules, usually
4、 circular exist independently of host chromosome autonomously replicating (replicon) may disappear spontaneously or by induction (UV) incompatibility and compatibility,Classification of Plasmids,Transfer properties Conjugative 40-100kbp eg. F, R plasmid Nonconjugative 15kbp, transfer by mobilization
5、 eg. ColE1 plasmid,Phenotypic effects Fertility plasmid,F plasmid coding sex pilus,R determinant,Resistance plasmid, R plasmid resistance transfer factor resistance determinant,Virulence plasmid Coliciogenic plismid,3 Bacteriophage, phage,T4 bacteriophages infecting E.coli.,Bacteriophage (Phage),Def
6、inition Bacterial virus. Virus of bacteria, fungi, actinomyces, and spirochete.,Composition Nucleic acid DNA or RNA Protein Protection Infection,Composition and Structure,Structure (T4) Head or capsid Tail,Infection of Host Cells,Attachment Sheath contraction Nucleic acid injection,Attachment and in
7、jection,Types of Bacteriophage,Lytic or virulent phage (e.g., T4) Lysogenic or temperate phage (e.g., l),Virulent Phage,Lytic or virulent phage Phage that can only multiply within bacteria and kill the cell by lysis. (e.g., T4),Lytic Phage Multiplication Cycle,Lytic cycle,Attachment Injection and un
8、coating Biosynthesis Eclipse Early proteins Phage DNA synthesis Late proteins Intracellular accumulation Maturation and releasing,Lysogenic Phage,Lysogenic or temperate phage: Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. (e.g., l) Prophage Lyso
9、gen,Lysogenic bacterium Lysogenic conversion,Lysogenic bacterium /lysogen,prophage,Lysogenic phage /temperate phage,Lysogenic or phage conversion Definition: A change in the phenotype of a bacterial cell as a consequence of lysogeny Modification of Salmonella O antigen Toxin production by Corynebact
10、erium diphtheriae,Lytic versus lysogenic infection by phage Lambda,4 Thransposable element,Concept Segments of DNA that are able to move around the genome. Properties “Random” movement Jumping genes or movable genes First discovered in the 1940s by Barbara McClintock during her study on maize geneti
11、cs.(won the Nobel prize in 1983),Types of Transposon,Insertion sequences (IS) A short sequence of DNA containing only the genes for those enzymes required for its transposition.,IR: inverted repeat,Importance Mutation Plasmid insertion,Types of Transposon,Transposons (Tn) or complex Tn contain genes
12、 other than those required for transposition (eg. Antibiotic resistance or toxin genes),Importance Antibiotic resistance,II mechanism of variation,Mutation Gene transfer and recombination,i Mutations in bacteria,Changes in DNA sequences Base substitutions, deletions, insertions, rearrangements Spont
13、aneous mutation: 10-8-10-6 Backword mutation or reverse mutation,ii Gene transfer and recombination,Transformation Transduction Conjugation Lysogenic conversion protoplast fusion,General Features of Gene Transfer in Bacteria,Unidirectional Donor to recipient Donor does not give an entire chromosome
14、Gene variation can occur between species,1 Transformation,Definition: Gene transfer resulting from the uptake of DNA from a donor. Competence of the recipient (Bacillus, Haemophilus, Neisseria, Streptococcus),Griffiths transformation experiments,Bacterial Transformation With DNA Fragments,2 Conjugat
15、ion,Definition: Donor DNA transferred to recipient cell through sex pilus.,F plasmid,Mechanism of F+ x F- Crosses Pair formation Conjugation bridge DNA transfer Origin of transfer Rolling circle replication,F plasmid,Hfr, high frequency of recombination,Physiological States F plasmid,F plasmid,Mecha
16、nism of Hfr x F- Crosses,Mechanism of F x F- Crosses,Resistance plasmid, R plasmid,RTF (resistance transfer factor) transfer genes code pili R determinant (resistance determination ) resistance genes transponsons,3 Transduction,Definition: Gene transfer from a donor to a recipient by way of a bacteriophage,Types of transduction,Generalized - Transduction in which potentially any donor bacterial gene can be transferred Specialized (restricted) - Transduction in which only certain
